This study analyzed the composition of atherosclerotic plaques in the 4 major epicardial coronary arteries in 8 women <40 years of age (mean 34) with fatal coronary artery disease (CAD) and compared these data to previous studies of 37 adults >45 years of age (mean 59) with fatal CAD. Using a computerized morphometry system, analysis of the 4 major epicardial coronary arteries showed the major component of plaque to be a combination of cellular (mean percent total plaque area= 65%) and dense (19%) fibrous tissue. Arterial segments narrowed >75% in cross-sectional area from these young women when compared to similarly narrowed arteries from 37 older patients (32 men [86%]) with fatal CAD showed significantly more cellular fibrous tissue and lipid-rich foam cells and less amounts of dense fibrous and heavily calcified tissue. The large amount of lipid-containing foam cells and relative lack of acellular scar tissue in coronary plaques in these young women suggests a greater potential for reversibility of these plaques in this subset of patients with CAD.